The technology of the present disclosure relates generally to distributed antenna systems (DASs) that support distributing communications services to remote units, and particularly to individualized automatic level control of remote units based on their respective contributions to combined uplink power.
Wireless communication is rapidly growing, with ever-increasing demands for high-speed mobile data communication. As an example, local area wireless services such as WiFi and wide area wireless services are widely deployed. Distributed communications systems communicate with wireless devices called “clients,” “client devices,” or “wireless client devices,” which must reside within the wireless range or “cell coverage area” in order to communicate with an access point device. DASs are particularly useful to be deployed inside buildings or other indoor environments where client devices may not otherwise be able to effectively receive radio-frequency (RF) signals from a source, such as a base station for example. Example applications where DASs can be used to provide or enhance coverage for wireless services include public safety, cellular telephony, wireless local access networks (LANs), location tracking, and medical telemetry inside buildings and over campuses.
One approach to deploying a DAS involves the use of RF antenna coverage areas. Antenna coverage areas can be formed by remotely distributed antenna units, or remote units (RUs). The remote units each contain or are configured to couple to one or more antennas configured to support the desired frequency(ies) or polarization to provide the coverage areas. Antenna coverage areas can have a radius in the range from a few meters up to twenty meters. Combining a number of remote units creates an array of antenna coverage areas. Because the antenna coverage areas each cover small areas, there typically may be only a few users (clients) per antenna coverage area. This arrangement generates a uniform high quality signal enabling high throughput supporting the required capacity.
As an example, FIG. 1 illustrates distribution of communications services to coverage areas 10(1)-10(N) of a DAS 12, wherein ‘N’ is the number of coverage areas. These communications services can include cellular services, wireless services such as RFID tracking, Wireless Fidelity (WiFi), local area network (LAN), WLAN, and combinations thereof, as examples. The coverage areas 10(1)-10(N) may be remotely located. In this regard, the remote coverage areas 10(1)-10(N) are created by and centered on remote antenna units 14(1)-14(N) connected to a central unit 16 (e.g., a head-end controller or head-end unit). The central unit 16 may be communicatively coupled to a base station 18. In this regard, the central unit 16 receives downlink communications signals 20D from the base station 18 to be distributed to the remote antenna units 14(1)-14(N). The remote antenna units 14(1)-14(N) are configured to receive downlink communications signals 20D from the central unit 16 over a communications medium 22 to be distributed to the respective coverage areas 10(1)-10(N) of the remote antenna units 14(1)-14(N). Each remote antenna unit 14(1)-14(N) may include an RF transmitter/receiver (not shown) and a respective antenna 24(1)-24(N) operably connected to the RF transmitter/receiver to wirelessly distribute the communications services to client devices 26 within their respective coverage areas 10(1)-10(N). The remote antenna units 14(1)-14(N) are also configured to receive uplink communications signals 20U from the client devices 26 in their respective coverage areas 10(1)-10(N) to be distributed to the base station 18. The size of a given coverage area 10(1)-10(N) is determined by the amount of RF power transmitted by the respective remote antenna unit 14(1)-14(N), the receiver sensitivity, antenna gain and the RF environment, as well as by the RF transmitter/receiver sensitivity of the client device 26. Client devices 26 usually have a fixed RF receiver sensitivity, so that the above-mentioned properties of the remote antenna units 14(1)-14(N) mainly determine the size of their respective remote coverage areas 10(1)-10(N).
In the DAS 12 in FIG. 1, the uplink gain in each remote antenna unit 14(1)-14(N) determines its sensitivity. Higher gain provides higher sensitivity (i.e., increased ability to decode weak uplink communications signals 20U). Each unit 14(1)-14(N) in the DAS 12 in FIG. 1 may include automatic level controllers (ALCs) 28(1)-28(N) that limit the power level of the received incoming uplink communications signals 20U to a predetermined power level. The ALCs 28(1)-28(N) can be used in the remote antenna units 14(1)-14(N) to avoid strong incoming uplink communications signals 20U overloading the communications signal processing circuitry (e.g., an amplifier) and distorting the uplink communications signal 20U. As another example, if the DAS 12 is an optical fiber-based DAS in which the remote antenna units 14(1)-14(N) convert the uplink communications signal 20U to optical uplink signals, a strong uplink communications signal 20U could overload the laser diode (not shown) used to convert the uplink communications signal 20U to optical uplink signals.
Further, the multiple received uplink communications signals 20U arriving at the remote antenna units 14(1)-14(N) are summed in the central unit 16. However, it may also be desired that the summed multiple received uplink communications signals 20U in the central unit 16 not exceed a defined threshold aggregated power in the central unit 16 or at the base station 18. Even though the individual signal level of each received uplink communications signals 20U in the remote antenna units 14(1)-14(N) can be controlled by the ALCs 28(1)-28(N) to be within power level limits of the individual remote antenna units 14(1)-14(N), the power level of the combined uplink communications signals 20U may be high enough to overload the signal processing circuitry in the central unit 16. Thus, to keep the combined uplink communications signals 20D in the central unit 16 below a desired maximum power level, the ALCs 28(1)-28(N) in the remote antenna units 14(1)-14(N) can be controlled to reduce the gain level of the individual uplink communications signals 20U received in each remote antenna unit 14(1)-14(N). However, the sensitivity of the uplink paths in the remote antenna units 14(1)-14(N) are reduced as a result. This may result in the signal level of a particular uplink communications signal 20U within a given remote antenna unit 14(1)-14(N) being lower than desired for processing within the remote antenna unit 14(1)-14(N) and/or not reaching the base station 18 with enough power.
Therefore, this creates a dilemma in that gain set by the ALCs 28(1)-28(N) must be set high enough to achieve the desired sensitivity but also avoid the combined uplink communications signals 20U from overloading the central unit 16 and/or the base station 18. The gain set by the ALCs 28(1)-28(N) may also need to be set high enough to allow uplink signals 20U to reach the central unit 16 and base station 18 without enough power.